thomas



W. V. TURNER AND T. H. THOMAS.

REGENERATIVE BRAKING SYSTEM.

APPLICATION FILED FEB. 5, 1916.

I 1,322,844. Patented Nov. 25, 1919.

gig-,1

v UNITED STATES PATENT OFFICE.

WALTER V. TURNER, OF WILKINSBUBG, AND THOMAS H. THOMAS, 0F EDGEWOOD,PENNSYLVANIA, ASSIGNOBS TO THE WESTINGHOUSE AIR BRAKE COMPANY, OFWILMERDING, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

REGENERATIVE BRAKING SYSTEM.

T 0 all whom it may concern:

Be it known that we, WALTER V. TURNER and THOMAS H. THOMAS, citizens ofthe United States, residing at, respectively, VVilkinsburg and Edgewood,in the county of Allegheny and State of Pennsylvania, have jointlyinvented a certain new and useful Improvement in Regenerative BrakingSystems, of which improvement the followingis a specification.

In electric traction systems where direct current is employed forpropelling the vehicles, it is well known that the motors may serve asgenerators when driven by the momentum of the vehicle, and that suchgenerated current, or a portion of it, may be returned to line conductoror source of supply if the current generated is at a voltagesufficiently greater than the line voltage, and that when operating inthis manner, the generator also serves as a brakingelement for retardingthe vehicle when descending grades or for deceleration when running on alevel track. Such regenerative ,braking systems have not, however,heretofore proved to be very efficient either in braking nor in theamount of current restored, on account of the comparatively limited timeat which vehicle is being driven by its momentum at a sufficiently highrate of speed to overcome the voltage of the line.

If a direct current motor when being driven by the momentum of thevehicle at a given speed is restoring a certain amount of energy to theline and thus acting as a braking generator to retard the Vehicle, it isapparent that, as the speed decreases, the

I induced voltage of the motor also dim1n ishes, and consequently lessand less current is returned to the line until the induced voltage fallsto that of the line when further regeneration is impossible, and thebraking effect ceases. If, notwithstanding the diminishing speed of thevehicle, the regenerated voltage could be maintained above the linevoltage, some current could be restored to the line, or distributingsystem, throughout a much longer eriod of time, and the braking effectcould be utilized until the vehicle is brought nearly to a completestandstill.

One of the objects of this invention, therefore, is to provide meanswhereby the voltage generated by the motors acting as Specification ofLetters Patent.

Patented Nov. 25, 1919.

Application filed February 5, 1916. Serial No. 76,237.

time the air brakes may be employed to complete the stop.

Where a plurality of motors are employed, such as a four motorequipment, for propelling the vehicle, and the motors are acting asgenerators driven by the momentum of the vehicle, the maximum voltagefor a given speed will be developed when the motor-generators areconnected in series, while only half this voltage will be developed atthe same speed when they are connected in series parallel, and stillless voltage when they are connected in full parallel. In order tocompensate for the reduction in speed and maintain the higher voltageoutput from the motor-generators, one of the features of our improvementcontemplates theautomatic changing of the motor connections fromparallel at high speed to series-parallel and then to full series as thespeed diminishes, whereby the high voltage may be kept up during themajor portion of the stopping period.

Another feature of our improvement com prises the use of a booster, orequivalent means, in series with the generator circuit for raising thevoltage therein to compensate for the diminishing speed .of thegenerators during the respective periods that the same are connectedeither in parallel, orin series-parallel, or in series, the booster being driven by any suitable means, and operating to automaticallymaintain the voltage either by varying the strength of its field, orby-varying the speed of the driving motor.

According to another feature of our invention, the air brake system iscombined with the regenerative system to produce certain results, sinceit will be evident that when operating at slow speeds and when theregenerated current falls below a predetermined amount, as whencompleting a stop,

it is desirable that the air brake be used, and our improvementtherefore also contemplates means for automatically applying the airbrake when the regenerated current falls to a certain minimum.

As a feature of safety,.it is desirable that at the time ofregeneration, there should be master control braking position, or may beoperated by a separate switch handle,

to the propelling system in any suitable or is well understood byallowed at such grammatically, a four motor comprising armatures, A A;A, A, con-F a limit to the maximum u on certain a ong the roa speedpermissible rades, and at various points 5, so that the maximum speedair brakes alone could properly control the train, it for an reason, theregenerative system should in With this in view, our improvement furthercontemplates a provision for automatically a plying the air brakes incase the speed 0 the vehicle exceeds the desired maximum at thetime'that the regenerative system is justing this maximum allowablespeed according to the grade or other conditions of the track.

The features of our improvement are adapted to be carried'out in avariety of different forms, and we do not therefore limit ourselves orparticular construction of parts.

In the accompanying drawing, the figure illustrates, in diagram, oneform of regenerative 'brakin system embodying our improvement, anapplied to a vehicle with a four motor equipment.

The electric connectionsincluding [the I circuits, controllers,switches, etc, for controlling the motors in propelling the ve hicle,are not shown in the drawing, and onlya sufiicient number of contactsrepresenting a brake switch or controller, 2, are shown connected to thelocal or regenerative circuits of the motors, as are necessary toillustrate the operations during the regenerative braking periods. Thecontacts of the brake switch, 2, are indicated in the closed is moved toopen the propelling cirup the motors to act as regenerative circuit forand for restoring energy generators in. the braking purposestotheliney';

It will bejunderstood that the contacts for the brake switch, 2, may bemounted upon or operated b the running controller or er when turned to acertain or be connected u preferred manner, and it is not deemednecessary to further illustrate the circuits and control of saidpropelling system, since'it those familiar with the art as to how theregenerative system,

as herein illustrated, ma be properly con nected into the propellingmotors.

, In the drawing, we have illustrated, dianected "by suitable leads, A,B C,

G and H, through contact ries-paralle regu ating or change 'over switch,3, and motor fields, F, F, F,- F,

points will be such that the v in operation, and also means for manuallya to any specific arrangement position to which this erative brakingswitch, 2.

system of the I equipment I .ftions which v bars on switch, 2, withcorres ondm contact fingers of-a se having leads, J, K, L, M, N, O, P,Q, suita'bly connected through corresponding contact bars on switch, 2,when in braking position. The change over switch, 3, may be operated byvarious forms of speed controlled means which serve to shift therelation of the generators according to certain variations in the speedof the vehicle the means, as shown, com rising a centri ugal overnor, 3,the sha t of which ma be driven from an axle of the vehicle an operate;through lever, 6, to open and close the valves, 6' and 6", forcontrolling the supply of fluid to and exhaust from the 15- tons, 7 and7, of cylinder, 7. A partition, 7, divides the cylinder into "separatechambers for the respective pistons, the piston, 7, being connected toactuate the switch, andhaving a spring, 7, opposing the action of thefluid pressure.

When the vehicle is traveling at or above a certain speed, at which thegovernor raises the lever, 6, to close the exhaust and open both valves,6 and 6", to admit both istons, 7 and 7", the switch, 3', is held in ful'parallel position, as shown in the drawing. When the s ciently toclose one va ve, 6, and open the exhaust from piston, 7, the s ring, 7,shifts the switch to the series-para lel position, at which point thepiston, 7', engages iston, 7 and is held until the speed is iirtherreduced sufliciently for the governor to close valve, 6', and 0 en theexhaust from piston, 7", whereupon the spring moves both pistons and theswitch to the series position,

A booster,4, is employed for raisingthe Voltage of the regeneratedcurrent from the motor generators sufiiciently above the line voltage toreturn current to the line, and to maintain the regenerated voltage asthe .spee'd diminishes, the booster being driven b a motor, 4, withcurrent from the line tli rough the wire, R, leading from the regen- Oneof the armature terminals of the booster is connected to thereturn lead,H, from the generators, the

p other armature terminal being connected by wire, S, with the line, T,through a contact bar on regenerative switch, 2. The field of thebooster is energizzed by current from the line through wire, and may becontrolled- -.by a rheostat, 13, governed by the solenoid or magnet, 12,inserted in the regenerative circuit wire, S, whereby the strength ofthe booster field may be automatically adjusted by said regeneratedcurrent to maintain a substantially constant current regardless offluctuations in line voltage or other condimight vary the output of thegenerators. The booster is also governed by the speed of the vehicle inorderto compen: sate for the reduction in speed during the respectiveperiods that the motors arev n-' nected up in theirdifierent renews yfluid to I eed diminishes sufiiin the field circuit of the motor, 4, therheostat beingcontrolled by the speed governor,

3. .As shown in the drawing, a carbon'rheostat is employed havingalever, for exerting a varying pressure on the carbon disks to vary theresistancein the fields of the motor, 4.- A spring, 3, acts upon lever,"5 tending to diminish the pressure upon. v

tabl1sh1ng the regenerative circuits. For the a the carbon rheostat, andthereby increase the resistance, theforce of the spring, 3", be-

ing regulated by the, movement of the weights of the governor, 3.-Another spring, 8, acts on the lever, 5, in thecopposite direction andtends to increase the pressure on thecarbon rheostat, The effectivepressure acting on the rheostat is, therefore, the (hi ference betweenthe force of the springs, 3' and 8, and as the shifting of the governorweights, due to variation in speed, also varies the force of the spring,3, the resistance of the rheostat, and consequently the speed of the.motor, 4, is accordingly regulated to compensate 'for the diminishingspeed of the motor generators. In order to continue this regulationthrough each period of re eneration for the different positionsof t echange over switch, 3 other springs, 8 and 8- are mounted to act on thelever, 55, but are held out of operation by means of the pistons, 8 and8", when the changeover switch is in full parallelposition, the valves,6" and 6?, also controlhng the supply of fluid to these pistons. Whenthese valves are operated by the governor,

to release fluid from the pistons, 7 and 7",

fluid is also releasedfrom istons, 8 and 8",

thus throwing the force 0 the springs, 8 and 8', onto the lever, 5". Thecoil of the magnet valve, 9, is insert- .ed in the return wire, S,sothat when the speed of the vehicle and the corresponding regeneratedcurrent has diminished, to 'a predetermined low amount, this valve isauto matically opened to vent air-{from a pipe of the air brake system,and cause anapplication of the air brakes toJcomplete the stop. Anothervent valve, 10*, is'arranged to be op erated to likewise vent air fromthe pipe of the air brake system when the speedofthe vehicle exceeds apredetermined maximum degree, such vent valve being convenientlyactuated by the'governor through a'lever, 10, and a rod, 10, connectingthe same with the lever, 61 This maximum speed may be adjusted to anypoint desired by means of the hand lever device, 11, connected to shiftthe fulcrum of lever, 10. It is preferred that this device be soadjusted as to cause an automatic application of the air brakes wheneverthespeed of thevehicle exceeds what may be safely controlled by means ofthe air brakes without the assistance of the. regen- Eerative brakingsystem. I

Communication from'the pipe, 15, of the air brake system to the ventvalves, 9 and 10*, is preferably controlled by a valve, 18, operatedmanually at the same time that the regenerative braking switch, 2, isthrown, andprefer'ably attached thereto, whereby saidcommunication isout off when the brake swltch is turned to the running position, and

opened when the brake switch is thrown to the position shown in thedrawing for 'espu rposeiof cutting off the regenerative circuits whenthe speed of the vehicle has reduced'to the minimum, atwhich the ventvalve,9, is opened, a switch, 10, is inserted in the return wire, H,from the generators, the switch being held closed by piston, 10*,

and air admittedthrough valve, 18, from the automatically opens. theclrcuit, H. The

maximum speed vent valve, l 0*,-is, however, preferably s0 connected asto reduce the air pressure for causingan application of the air brakes,but not to release the pressure from piston, 10 The switch, 10, thusremains closed at that time so that the comblned braking effect from theregenerative system and the air brake'system is produced; As soon as thespeed is reduced to the predetermined safe amount for which theapparatus 1s adjusted, the vent valve, 10, closes,

and the air brakes are automatically 're leased, thus limiting the speedof thevehicle duringvthe regenerative period.

When the brake switch is in running position, the; vent valves, 9 and10", are cut oil from thepipe ofithe air brake system, by means of thevalve,'18, which'tu'rns with the brake switch, but in brakingposition,as shown, communication is established from the pipe, 15, of the airbrake system to both valves, 9 and 10, and also from the fluid pressurepiston, 10*, to the vent valve, 9.

The regenerative circuit switch, 10, is, there-- sure acting on piston,'1O

fore, normallyheld closed by the air pres- Whenthe' vehicle is running,and it is de sired to make a brake application, the brake switch,' 2, isthrown to braking thereby connecting up the motors to .act'as generatorsin the regenerative circuit, to rea, store, current to the line, T. 'Thechange izo over "switch, 3",the'n"occupies one of its positions deending upon the speed. of, the 've hicle an of the governor, 3. The,armature of the booster, 4', is connected in series with,

the regenerative circuit through leads, H and S, while current from thelinefiows to the fields'of the booster and to the'armature v and fieldsof the motor, 4",thro11ghthe wire, B. Let us suppose that-the speedof-the vetures, A A A, A, of the '3", and transmitted to .5, will bethat whic hicle and governor, 3, at this time is sufficiently great tohold the change over switch, 3, in its full parallel position, asindicated, the course of the regenerated current is then from oneterminal of the armaenerators in parallel to the return wire, switch,10, throu h the armature of the booster, 4, wire, S, including the coilsof the electromagnets 12 and 9, to contact bar on brake switch, 2, toline, T, and return by ground connection to the negative terminals ofthe armature of the generators. As shown in the drawings, the fields, FF F and F, of the generators, are at this time connected in seriesbetween the line and the ground by the leads,

K, L, M, N, O, P, Q, and the contact bars on the brake switch, althoughthe circuits may be connected in other ways, if preferred. If theregenerated current rises higher than a certain amount, the force of themagnetic pull of the core of the magnet, 12, acting on the lever, 12,will be increased and the pressure of spring, 12 on the carbon rheostatdiminished, so that less current from ,the line will flow through therheostat and the fields of the booster, 4, will be correspondinglyweakened, thus regulating the booster to decrease the amount of currentflowing back to the line. This feature serves to keep the current flowproperly balanced at all times. With the speed at the rate as aboveindicated, the weights of the governor, 3, move out radially to aposition in which the lever, 6, clears the valves, 6" and 6", and acertain tension is exerted upon the spring,

the lever, 5", actin upon the carbon rheostat, 5. With the valves, 6 and6", in the positions shown, the exhausts are closed, and fluid pressureis admitted to all of the pistons, 7, 7*, 8 and 8, thereby relieving thelever, 5", from the force of the'springs, 8 and 8", so that theeffective pressure actin on the carbon rheostat, is produced by springs,8 and 3*.

As the speed of "the vehicle begins to diminish,due to the retardingefl'ect produced by the generators in re enerating current and'restoringsame to t e line circuit, the governor weights move inward\and therebytend to increase the force of the spring, 3". This has the efi'ect ofvarying the pressure of lever 5*, upon the carbon rheostat, 5, andthereby regulating the motor, 4, driving the booster, 4, so as tocompensate for the diminishing speed of the vehicle and the gen- Ierators, and maintain the voltage of the regenerated current above thatof the line circuit. As the speed continues to diminish, the furtherinward movement of the governor weights serves to depress the lever, 6,sufficiently to operate the valve, 6, to close its supply port and openits exhaust port, whereupon the fluid is released from pistons,

.to open t e reg 7 and 8'. The spring, 7, then moves the piston, 7,downward against the stem of piston, 7", and throws the switch 3, to itsseries-parallel position, whereby the voltage generated will beincreased, and thereby compensate for the diminished speed of thevehicle. In order to make a corresponding reduction in the speed of thebooster to maintain the voltage of the regenerated current substantiallyconstant, the sprin 8, is released and exerts its ressure on fever, 5,and rheostat, 5. The eld of the motor, 4, is thereby strengthened andthe speed of the booster reduced the desired amount. The current willthen be restored to the line throughout another period of furtherreduction in the speed of the vehicle, during which period theregulation of the motor, 4, of the booster, by means of rheostat 5,spring, 3, and governor, will be repeated as before described.

As the speed continues to decrease, the vovernor weights move fartherinward, and depress the lever, 6, to operate the valve, 6", therebyreleasing fluid 8". T e spring, 7, then moves the piston fartherdownward, and throws the switch, 3, to the full series position, thusagain raising the voltage of the regenerated current. The spring 8, isreleased by the exhaust of fluid from the piston, 8", and adds its forceto that of springs, 8 and 8 acting on the lever, 5, thus again adjustingthe rheostat, 5, to reduce thespeed of the motor, 4, and booster, 4, tocorrespond with the changed relation of the' l'generators.

The voltage of the regenerated current is thus maintainedhigh enough toflow to the line circuit throughout nearly the full stopping eriod, butwhen the'speed is reduced to sue a low rate that the current fails tohold the magnet valve, 9, closed, this valve opens to vent air from thepipe, 15, and ef' fect an a plication of the air brakes to complete t estop. The fluid will also be released from the piston, 10", at the sametime, and the s ring, 10, operates the switch, 10, erative circuit toprevent back flow of cunrtant from the line.

If, at the timethe brake switch is turned to braking position, the speedof the vehicle is in excess of the desired maximum, as determined by theadjustment of the device, 11, the vent valve, 10, will be immediatelyoperated by the governor to discharge air from the air brake s stem andeffect an application of the air brakes. The regenerative braking effectwill also be obtained, and the combined action of the two brakingsystems will soon reduce the speed to a safe amount.

If it be desired to produce a shorter stop at the time of regeneration,the usual air brake system may be employed for such pur ose.

aving now described our invention, what from pistons, 7" and we claim asnew and desire to secure by Letters Patent is:

1. A regenerative braking system comprising a plurality of motors,adapted to act as momentum drlven generators, a brake switch momentumdriven generators, a brake switch ing'a plurality of motors,

having contacts for connecting up the generators to restore current to:the line, a booster located in the circuit between said generators andthe line, and electro-magnetic means governed by the regenerated currentfor regulating the resistance in the field circuit of thebooster.

3. A regenerative braking system comprising a plurality of motors,adapted to act as momentum driven generators, a brake switch havingcontacts for connecting up the generators to restore current to l theline, a booster located in the circuit between said generators and theline, a motor for driving the booster, and means governed by the speedof the vehicle for controlling said motor.

4. A regenerative braking system comprising a plurality of motors,adapted to act as momentum driven'generators, a brake switch havingcontacts for connecting up the generators to restore current to theline, a booster located in the circuit between said generators and theline, a motor operated by current from the line for driving the booster,and means governed y the speed of the vehicle for controlling resistancein the motor circuit.

5. A regenerative braking system comprisadapted to act as momentumdriven generators, a brake switch having contacts for connecting up thegen-- erators to restore current to the line, a seriesparallel switchgoverned by the speed of the vehicle for shifting the relation of thegen erators, and a booster for maintaining the volta e in theregenerative circuit.

6. i regenerative braking system comprising a plurality of motors,adapted to act as momentum riven generators, a brake switch havingcontacts for connecting up the generators to restore current to theline, a series-parallel switch governed by the speed of the vehicle forshifting the relation of said generators, a booster located in thecircuit between the generators and the line, and means governed by thespeed of the vehicle for controlling said booster.

7. A regenerative braking system comprising a plurality of motors,adapted to act as as momentum driven generators, a brake switch havingcontacts for connecting up the generators to restore current to theline,

a series-parallel switch governed by the speed of the vehicle forshifting the relation of said generators, a booster located in thecircuit between the generators and the line, an electro-magnetic meansgoverned by the regenerated current for regulating said booster.

8. A regenerative braking system comprising a plurality of motors",adapted to act as momentum driven generators, a brake switch havingcontacts for connecting up the generators to restore current tothe line,a seriesparallel switch governed by the speed of the vehicle forshifting the relation of said generators, a booster located in thecircuit between the generators and the line, amotor operated from theline for driving said booster, and means governed by the speed of thevehicle for controlling sald motor.

9. In a regenerative braking system, the combination of a plurality ofmotors, adapted to act as momentum driven generators, a brake switchhaving contacts for connecting up the generators to restore current tothe line, a series-parallel switch for shifting the relation of saidgenerators, a fluid pressure device for actuating said seriesparallelswitch, and means governed by the speed of the vehicle for controllingthe fluid pressure.

10. In a regenerative braking system, the combination of a plurality ofmotors, adapted toact as momentum driven generators, a brake switchhaving contacts for connecting up the'generators to restore current tothe line, a series-parallel switch for shifting the relation of saidgenerators, a cylinder and piston for actuating said seriesparallel'switch, a valve for controlling the supply of fluid pressure to saidcylinder, and a speed governor driven by the momentum of the vehicle foroperating said valve.

11. In a regenerative braking system, the combination ofa plurality ofmotors, adapt-' ed to act as momentum driven generators, a brake switchhaving contacts for connecting up the generators to restore current tothe line, a series-parallel switch for shifting the relation of saidgenerators, a motor driven booster for maintaining the voltage of theregenerated current, a regulating device governed by the speed of thevehicle for com trolling said motor-booster, and means, also governed bythe speed, for shifting said series-parallel switch and for adjustingthe booster.

12. In a regenerative braking system, the combination of a plurality ofmotors, adapted to act as momentum driven generators, a brake switchhaving contacts for connecting up the generators to restore current tothe line, a series-parallel'switch for shifting the relation of saidgenerators, a motor driven booster for maintaining the voltage of theregenerated current, a regulating device governed by the speed of thevehicle for controlling said motor-booster, fluid pressure ap aratus foractuating said series-para lel switch and for adjusting the booster, andvalve means governed by the speed or the vehicle for controlling thesupply of fluid to said a paratus. 1

13. n a regenerative braking system, the combination of a plurality ofmotors, adapted to act as momentum driven generators, a brake switchhaving contacts for connecting up the generators to restore current tothe line, a series-parallel switch for shifting the relation of saidgenerators, a motor driven booster for maintaining the voltage of theregenerated current, a regulatin device governed by the speed of thevehic e for controlling said motor-booster, and means also governed bythe speed for shifting said series-parallel switch and for adjusting thespeed of the booster motor.

14. In a regenerative braking system, the combination of a plurality ofmotors, adapted to act as momentum driven generators, a brake switchhaving contacts for connecting up the generators to restore current tothe line, a series-parallel switch for shifting the relation of saidgenerators, a motor driven booster for maintaining the voltage of theregenerated current, a 'regulatin device governed by the speed of the ve1c le for controlling said motor-booster, fluid pressure apparatus foractuating said seriesparallel switch and for adjusting the speed of thebooster motor, and valve means governed by the speed of the vehicle forcontrolling the supply of fluid to said apparatus.

15. In a regenerative braking system, the combination of a plurality ofmotors, adapted to act as momentum driven generators, a brake switchhaving contacts for connecting up the generators to restore current tothe line, a series-parallel switch for shifting the relation of saidnerators, a motor driven booster for maintaining the voltage of theregenerated current, a spring operated regulatl device governed by thespeed for control ing the motor-booster, and means also governed by thespeed for shifting said series-parallel switch and for adjusting theeflective spring pressure of said regulating device.

16. In a regenerative braking iytem, the combination of a plurality omotors, adapted to act as momentum driven generators, a brake switchhaving contacts for connecting up the generators -to restore current tothe line, series-parallel switch for shifting the relation of saidgenerators, a

motor driven booster for maintaining thevoltage of the regeneratedcurrent, a spring operated regulating device governed by the speed ofthe vehicle for controlling said ators, and a brake switch havingcontacts for connecting up the generators to restore current to theline,.of an air brake system, and automatic means for causing anapplication of the air brakes when the speed of the vehicle is reducedto a predetermined minimum.

18. In a regenerative braking system, the combination with a pluralityof motors, adapted to act as momentum driven generators, and a brakeswitch having contacts for connecting up the generators to restorecurrent to the line, of an air brake system, and means governed by theregenerated current for effecting an application of the air brakes whenthe speed of the generators is reduced to a predetermined minimum.

19. In a regenerative braking system, the combination with a pluralityof motors, adapted to act as momentum driven generators, and a brakeswitch having contacts for connecting up the generators to restorecurrent to the line, of an air brake system, a vent valve for effectingan application of the air brakes, and an electromagnet governed b theregenerated current for actuatin sai vent valve.

0. In a regenerative braking system, the combination with a plurality ofmotors, adapted to act as momentum driven generators, and a brake switchhaving contacts for ling communication to said vent valve.

21. In a regenerative braking system, the combination with a pluralityof motors, adapted to act as momentum driven generators, and a brakeswitch having contacts for connecting up the generators to restorecurrent to the line, of an air brake system, and automatic means foreffecting an ap lication of the .air brakes when the ipeed of thevehicle exceeds a predetermine mum.

22. In a regenerative braking system, the combination with a pluralit ofmotors, adapted to act as momentum d riven generators, and a brakeswitch having contacts for connecting up the generators to restorecurrent to the line, of an air brake system a vent valve for eflectingan application 6% maxithe air brakes, and means governed by the speed ofthe vehicle for opening said vent valve when the speed exceeds apredetermined maximum.

23. In a regenerative braking system, the combination with a pluralit ofmotors, adapted to act as momentum riven generators, and a brake switchhaving contacts for connecting up the enerators to restore current tothe line, 0 an air brake system, a vent valve for effecting anapplication of the air brakes, mechanism operating to open said valvewhen the speed exceeds a predetermined maximum, and means for adjustingsaid mechanism to vary the maximum speed permissible.

24. In a regenerative braking system, the combination with a pluralityof motors,

adapted to act as momentum driven generators, and a brake switch havingcontacts for connecting up the generators to restore current to the hue,of an air brake system, a vent valve for effecting an application of theair brakes, a speed governor for opening said valve when the speedexceeds a certain maximum, and means for manually adjusting theconnection between said governor and the vent valve.

25. In a regenerative braking system, the combination with a pluralityof motors, adapted to act as momentum driven generators, and a brakeswitch having contacts for connecting up the generators to restorecurrent to the line, of an air brake system,

a vent valve to effect an application of the air brakes when the speedexceeds a predetermined maximum, and a valve movable with the brakeswitch for controlling communication from the brake system to said ventvalve.

26. In a regenerative braking system, the combination with a pluralityof motors, adapted to act as momentum driven generators, and a brakeswitch having contactsfor connectin up the generators to. restorecurrent to t e line, of an air brake system, means for effecting anapplication of the air brakes and for opening the regenerative circuitwhen the speed falls below a predetermined minimum.

27. In a regenerative braking system, the combination with a pluralityof motors, adapted to act as momentum driven generators, and a brakeswitch having contacts for connecting up the generators to restorecurrent to the line, of an air brake system a fluid pressure actuatedswitch normally closing the regenerative circuit when the brake switchis in braking position, and a magnet valve controlled by the current insaid circuit for releasing air from the brake system and from said fluidpressure switch. 28. In a regenerative braking system, the combinationwith a pluralit of motors,

adapted to act as momentum riven genera-' tors, and a brake switchhaving contacts for connecting up the generators to restore current tothe line, of an air brake system, a fluid pressure piston and switch forthe regenerative circuit, a vent valve for effecting an application ofthe air brakes and releasin fluid from said piston when the speed iallsbelow a redetermined minimum, and a valve movable with the brake switchfor controlling communication to said vent valve.

29. In a regenerative braking system, the combination with a pluralityof motors, adapted to act as momentum driven generators, and a brakeswitch having contacts for connecting up the generators torestore-current to the line, of an air brake-system, a fluid pressureactuated switch for there'- generative circuit, amagnet vent valvecontrolled by the regenerative current .fior releasing a1r from thebrake system and from said piston, and a valve movable with the brakeswitch for cutting off said vent valve from the brake system and fromsaid fluid pressure piston.

In testimony set our hands.

' WALTER V. TURNER. THOMAS H. THOMAS.

whereof we have hereunto

